1. Field of the Invention
The present invention relates to a magnetic recording medium. More particularly, it relates to a composition which constitutes a superior magnetic recording layer in a magnetic recording medium such as a video tape or a computer tape for which durability is required.
2. Description of the Prior Art
The magnetic recording medium such as a video tape or computer tape is brought in contact and frictional engagement with a magnetic head under a high speed, and the magnetic coating layer is likely to be damaged. Accordingly, a magnetic recording medium having superior durability is required. To meet this requirement, a magnetic recording medium has been proposed which has a magnetic coating layer containing from about 1 to about 25% by weight, based on the magnetic powder, of non-magnetic powder having a particle size of at most 5 .mu.m and a Mohs' hardness at least 6. With this magnetic recording medium, the abrasion resistance of the magnetic coating layer is sufficiently improved, but the abrasion of the magnetic head and the decrease in the S/N ratio become substantial, whereby it becomes very difficult to control the abrasion of the magnetic head or the decrease of the S/N ratio and in an extreme case, it is likely that the magnetic head is damaged or the surface of the magnetic head is roughened. Further, when such non-magnetic powder is used in a substantial amount, unwanted substances derived from the abrasion of a dispersing machine during the dispersing operation, are likely to be incorporated, whereby in many cases, the physical property of the binder will be modified and in an extreme case, the coating material tends to be gelled. Thus, when applied to a substrate such coating material has often led to an inferior finish of the surface or deterioration of the electromagnetic conversion characteristics.
Under the circumstances, the present inventors have conducted extensive researches to overcome such difficulties and as a result have found that when two specific types of non-magnetic powders having specific average particle sizes and surface areas are used as a mixture, it is possible to obtain far superior effectiveness as compared with the case where various non-magnetic powders heretofore are used.